1. Field of the Invention
This invention relates generally to improvements in cylinder lock and key systems and, more particularly, to hierarchical lock and key systems.
2. Description of the Prior Art
Yale type cylinder locks are well known and have been in continuous use since 1865. Typically, in such locks key differs are developed by adjusting incrementally the lengths of the bottom most pin tumblers and the corresponding bitting depths on the key. In addition, several techniques have been developed to arrange lock cylinders and their associated keys in hierarchical systems. For example, U.S. Pat. No. 369,628 to Van Hoevenbergh illustrates segmented pin tumblers disposed in one or more columns which allow several keys which are bitted differently from each other to operate a single cylinder. U.S. Pat. No. 420,174 to Taylor discloses non-rotatable pins with contact surfaces of different heights which permit different keys to operate the same cylinder. U.S. Pat. No. 564,803 to Stadtmuller discloses tumbler pins having dual vertical key contact surfaces operable by different keys. U.S. Pat. No. 567,305 to Donovan provides master keying capability through variations in the shape of the key profile and the corresponding keyway in the cylinder. U.S. Pat. No. 567,624 to Taylor provides master keying capability by using plate tumblers for changing the tumbler-key contact area which allows different keys to operate the same cylinder. In addition, U.S. Pat. No. 3,349,587 to Keller discloses a method of positional masterkeying.
Despite the many maserkeyed or hierarchical lock systems known in the art, there remains a need for new and improved lock cylinders that can be operated by more than one key. In large buildings and institutions, for example, cylinders and keys are often arranged in masterkeyed systems for the convenience of management personnel.
Interchangeable core cylinders are operable by a control key, and this permits a quick exchange of the core containing the tumblers for a core operated by a different key. See also the prior art currently classified in class 70, subclass 369 in the U.S. Patent and Trademark Office.
Cylinders also have been constructed which cooperate with different keys to allow for selective rotation of the barrels. See, for example, U.S. Pat. No. 4,107,966 to Schlage which discloses a cylinder that is partially operated by one key to retract a latchbolt, and is fully operated by another key to retract the latchbolt and a deadbolt.
Further, some lock cylinders are operable by a first key, but are adjusted when operated by a second key so as to render the cylinders operable only by the second key. See U.S. Pat. No. 3,099,151 to Schlage and the prior are currently classified in class 70, subclass 383 in the U.S. Patent and Trademark Office. The above-mentioned patents are only some examples of cylinders that are operable with different keys.
The positioning of tumbler pins by unique keys has been the subject of continuous improvement in the lock art. Patents issued for the great majority of lock cylinders now on the market have expired. Their keys can be copied on conventional machines of the type described in U.S. Pat. No. 1,439,382 to Segal. The keyblanks required are widely distributed beyond the control of the lock manufacturer. The development of skew cut bittings by Spain et al., as described in U.S. Pat. No. 3,499,302, provided additional security to the key owner because conventional rotary machines could not duplicate these angled cuts. However, as there have been machines developed to duplicate skew cut bittings, their security is reduced. Uniquely shaped bittings and controlled distribution of proprietary keyblanks reduces the odds that keys in the possession of dishonest employees can be copied at hardware stores and the like.
Notwithstanding improvements in the well worked lock arts, there remains a need for lock cylinders which can be operated by different keys and arranged in hierarchical systems. Such lock mechanisms should also resist contemporary lockpicking techniques, including impressioning methods to obtain false keys. It is also desirable that the dimensions of the lock not exceed conventional cylinder size. It is equally important that the components and the lock assembly can be economically mass produced.